The precedent for The Sabbath was absolutely set by the Creation week recorded in Genesis 1&2.
But there is a debate about if it was kept by believers as a custom before the Exodus. We have evidence of what animals are clean and unclean being known in Genesis. But nothing from Genesis 3 on through the first Passover that in any way alludes to Patriarchs or Hebrews keeping The Sabbath.
Now Exodus 16 which is the account of The Manna miracle is constantly cited as proof it was known before the giving of The Law. Indeed the Decalogue in Exodus 19 refers to it as something they already knew.
The thing is, if you study Exodus 16 carefully, it seems to be presenting this story as the origin of The Sabbath. Nothing in here suggests it was already being practiced.
On the 15th day of the Second Month, the Israelites complain. Then Moses tells them what is about to happen. This was BTW the month following the very first Passover.
At evening, when the 16th started, Yahuah's Glory appeared onto them and they eat Quail (and no vice president had to shoot anyone in the face). Then in the morning of that day they found the first Manna.
On the 6th day that the Manna fell they were instructed to gather twice what they usually did so they'd have Manna the following day which they were told not to collect Manna on. And thus that seventh day was named The Sabbath.
Now to many this would be an argument against Christians needing to keep it. I however see no correlation between what we have to keep and what came in with Moses, to me those issues are addressed elsewhere.
I'm writing this here because I feel understanding this could help us understand the Eschatological importance of The Sabbath. Because the Manna is often seen as another miracle repeated in Revelation in chapter 12.
If The Sabbath was a rule already. That would have to make this 15th of Iyar a Sabbath, but they don't seem to be keeping a Sabbath at the moment and no comment is made on it. Yahuah waits till it's Sunday to speak to the people.
If you counted hypothetical Sabbaths backwards from this. The 8th and 1st of that Iyar would have been Sabbaths.
And if the Nisan of the first Passover had 30 days, then it's Sabbaths would have been the 24th, 17th, 10th and 3rd. But if it had 29 days then they would have been the 23rd, 16th, 9th and 2nd.
The latter would happen to fit my model for the Nisan of the Crucifixion as a Thursday supporter. The former would happen to fit what is usually argued for by Wednesday supporters. But you can't get a Friday model from it. That doesn't prove anything but it's amusing. And either of those would put the hypothetical anniversary in advance of The Ascension on the 27th of Iyar, which might be interesting.
Maybe God arranged this so it would happen to fit where The Sabbath would haven been if it'd been being kept since Adam. But either way, I'm convinced now that the origin of The Sabbath as a custom kept by humans is in Exodus 16.
Nehemiah 9:12-15 also states that it was at this time that Yahuah made The Holy Sabbath known to them.